Apparatus and method for optimizing the level of RF signals based upon the information stored on a memory

ABSTRACT

A signal processing arrangement has a signal source for providing a radio frequency (RF) signal, a signal output point, and first control means coupled between the signal source and the signal output point for controlling the selection of a low noise figure amplifier in response to the magnitude of an RF signal on a tuned channel frequency and the magnitude of an RF signal in the vicinity of said tuned channel frequency.

This application claims the benefit under 35 U.S.C. §365 ofInternational Application PCT/US01/29807, filed Sep. 25, 2001, which waspublished in accordance with PCT Article 21(2) on Apr. 4, 2002 inEnglish; and which claims benefit of U.S. provisional application Ser.No. 60/235,038 filed Sep. 25, 2000.

The present invention concerns radio frequency (RF) signal processingarrangement and method for optimizing the level of RF signals, suitablefor RF signal receiving systems, such as television signal receivers.

It is desirable for a television signal receiver to receive televisionsignals which have proper signal strength throughout the entirebroadcast television band, so that a user can always enjoy good qualitypictures and sound. However, the signal strength of individualtelevision channels being received at a particular geographical locationoften varies from one another primarily due to the difference of thegeographical distance between each one of the broadcast stations and thereceiving location of the user. When the receiver tunes to a televisionchannel having undesirable signal characteristics (e.g., either too weakor strong interference present), such a condition could cause severalproblems including undesirable noise in the pictures due to poorsignal-to-nose ratio (S/N) and cross modulation caused by interferencefrom the adjacent frequency signals for analog reception. Moreover,these problems are especially harmful for the reception of digitalbroadcast signals since reception is totally lost when the quality ofthe signals falls below a particular threshold.

A conventional way to solve the weak signal problem is to selectivelyapply an additional amplifier optimized for low noise figure between anantenna and a tuner in response to the automatic gain control (AGC)signal, which represents the strength of the television signalsreceived. For example, The U.S. Pat. No. 5,638,141, entitled BROADCASTSIGNAL RECEIVER HAVING A LOW-NOISE AMPLIFIER INSERTED BEFORE A TUNER,filed by Bae et al., assigned to Samsung Electronics Co., Ltd., andissued Jun. 10, 1997 discloses this type of solution. Yet, theconventional solution is not a preferable solution to the problemsaddressed above because the AGC signal does not represent quality of thetelevision signals (i.e., picture and/or sound quality) but merelyrepresents the quantity (i.e., signal strength) of the television signalbeing received. Furthermore, the AGC signal does not reflect thestrength of the signals on the adjacent channel frequencies, which couldcause the interference problem. Therefore, a need exists for an RFsignal processing circuit which optimizes the level of input televisionsignals at each one of the television channels in response to thequality of the television signals and/or in response not only to thestrength of the tuned signal but also to that of the adjacent signals.

In accordance with an aspect of the invention, a signal processingarrangement comprises a signal source for providing an RF signal, asignal output point, and first control means coupled between the signalsource and the signal output point for controlling the magnitude of theRF signal in response to the magnitude of an RF signal on a tunedchannel frequency and the magnitude of an RF signal on a channelfrequency in the vicinity of the tuned channel frequency.

In accordance with another aspect of the present invention, a signalprocessing method comprising the steps of tuning to a channel frequency,retrieving information concerning RF signals on the tuned channelfrequency and a channel frequency in the vicinity of the tuned channelfrequency from a memory, and enabling an RF amplifier if the informationindicates that the magnitude of an RF signal on the tuned channelfrequency is below a first predetermined threshold level and themagnitude of an RF signal in the vicinity of the tuned channel frequencyis below a second predetermined threshold level.

In accordance with another aspect of the present invention, a signalprocessing method comprising the steps of tuning to a channel frequency,retrieving information concerning RF signals on the tuned channelfrequency and an RF signal in the vicinity of the tuned channelfrequency from a memory, and disabling an RF amplifier if theinformation indicates that either the magnitude of an RF signal on thetuned channel frequency is above a first predetermined threshold levelor the magnitude of an RF signal in the vicinity of the tuned channelfrequency is above a second predetermined threshold level.

These and other aspects of the invention will be described in detailwith respect to the accompanying drawings.

In the drawings:

FIG. 1 is a block diagram illustrating a portion of an analog/digitaltelevision signal receiver which includes a first exemplary embodimentof the signal processing arrangement in accordance with the principlesof the present invention;

FIG. 2 is a block diagram illustrating a portion of an analog/digitaltelevision signal receiver which includes a second exemplary embodimentof the signal processing arrangement in accordance with the principlesof the present invention;

FIG. 3 is a flow chart describing an exemplary manner of operation ofthe first embodiment as illustrated in FIG. 1 in accordance with theprinciples of the present invention; and

FIG. 4 is a flow chart describing an exemplary manner of operation ofthe second embodiment as illustrated in FIG. 2 in accordance with theprinciples of the present invention.

The exemplifications set out herein illustrate preferred embodiments ofthe invention, and such exemplifications are not to be construed aslimiting the scope of the invention in any manner. In the variousfigures, the same or similar reference designations are used to identifythe same or similar elements.

This application discloses a first signal processing arrangement whichcomprises a signal source, such as an antenna, for providing aninformation bearing RF signal, such as an analog and/or digitaltelevision signal, a signal output point, and control means, includingan attenuator and/or an amplifier such as a low noise figure amplifier,together with RF switches associated therewith, coupled between thesignal source and the signal output point for controlling the magnitudeof the information bearing RF signal in response to quality of theinformation borne by the RF signal. The signal processing arrangementmay further comprise determining means, such as a demodulator, coupledto the control means for determining the quality of the informationborne by said RF signal. According to an exemplary embodiment describedin detail below, such quality of the information is indicated by severalsignal parameters including automatic color control (ACC) level, pictureto sound ratio (P/S) for reception of analog television signals, andsignal to noise ratio (S/N), equalizer taps, and bit error rate (BER)for reception of digital television signals. A method performed by theforegoing arrangement is also disclosed herein.

Furthermore, this application discloses a second signal processingarrangement which comprises a signal source, such as an antenna, forproviding a RF signal, such as an analog and/or digital televisionsignal; a signal output point; and first control means, including anattenuator and RF switches associated therewith, coupled between thesignal source and the signal output for controlling the magnitude of theRF signal in response to the magnitude of the RF signal on the tunedchannel frequency as well as to that of an RF signal in the vicinity ofthe tuned channel, including one adjacent or near to the tuned channelfrequency. The signal processing arrangement may further comprise amemory for storing channel information concerning the magnitude of theRF signal for every receivable signal throughout a band of frequenciesincluding the magnitude of the RF signal for the channel being tuned andthose for the channels in the vicinity of the tuned channel, and secondcontrol means including a microprocessor coupled to the first controlmeans for controlling the first control means in response to the channelinformation stored on the memory. A method performed by this arrangementis also disclosed herein.

Referring now to the drawings, and more particularly to FIGS. 1 and 2,block diagrams 100 and 200 shows two exemplary implementations ofboost/attenuator circuits 110 and 210 respectively in conjunction withan analog/digital color television signal receiver. The foregoing firstand second signal processing arrangements, as well as the methodsperformed by the respective ones of the arrangements, are equallyapplicable to each one of the implementations illustrated in FIGS. 1 and2.

FIG. 1 discloses an exemplary implementation boost/attenuator circuit110 in conjunction with an analog/digital television signal receiver.Off-the-air digital and/or analog television signals are received at anantenna (not shown) and are then applied to RF input point 22 of U/Vsplitter 20 via an RF signal transmission line (not shown) such as acoaxial cable. U/V splitter 20 separates the UHF television signals fromthe VHF television signals in a frequency domain and supply the UHFtelevision signals to attenuator switch 118 which is part ofboost/attenuator circuit 110. Although FIG. 1 shows boost/attenuatorcircuit 110 being implemented in the UHF signal processing path, it canalso be implemented in the VHF signal processing path in the samemanner.

Attenuator switch 118 provides the UHF television signals to eitherattenuator 112 (e.g., 3 dB resistive RF attenuator) or to boost switch111 in response to an attenuator control signal from PLL IC 30 which isgenerated by microprocessor 50 and transmitted via the I²C bus. Boostswitch 111 receives the UHF signals from attenuator switch 118 andprovides them to either tunable single-tuned (ST) filter 114 ofboost/attenuator circuit 110 or to tunable signal-tuned (ST) filter 122,usually located at the input of the RF circuit in a television tuner ofthe television signal receiver, in response to a boost control signalfrom PLL IC 30 which is generated by microprocessor 50 and transmittervia I²C bus.

Tunable single-tuned (ST) filter 114 of boost/attenuator circuit 110attenuates the undesirable signals which might cause cross-modulationinterference. Filter 114 is designed with a wider bandwidth than typicalof a standard tuner input filter 122. Such a design reduces loss suchthat the noise figure performance of amplifier 116 is not significantlydegraded while affording some protection from interference. Tuningsignal ST for the filter is generated by digital to analog converter(DAC) IC 40 which is controlled by microprocessor 50 via the I²C bus.Tunable single-tuned (ST) filter 114 also operates as a tunableimpedance matching network between RF input point 20 and low noiseamplifier 116 to provide better impedance matching between the antennaand low noise amplifier 116 at a given frequency (e.g., a receivingfrequency). Better impedance matching improves the voltage standing waveratio (VSWR) between the antenna and low noise amplifier 116 resultingin reducing undesirable signal losses and impulse responses. Low noiseamplifier 116 is activated by the boost control signal from PLL IC 30which is generated by microprocessor 50 and transmitted via I²C bus.Although a fixed-gain amplifier is used as low noise amplifier 116 inFIG. 1, a gain-controlled amplifier may also be used with a proper gaincontrol circuit. The output signal of boost switch 111 is applied tosingle-tuned tunable filter 122.

UHF tuner circuit 120 includes tunable single-tuned filter 122,gain-controlled RF amplifier 124, tunable double-tuned (DT) filter 126,mixer 142, UHF local oscillator 146, and double-tuned (DT) IF filter152. The gain of gain-controlled RF amplifier 124 is controlled inresponse to the RF AGC signal generated by either analog video and soundprocessing circuit 60 (for analog signal reception) or by power detector179 (for digital signal reception). UHF tuner circuit 120 converts UHFtelevision signals to IF television signals and is usually located in atuner module of the television signal receiver.

The IF signals coming out of double-tuned IF filter 152 are thenprocessed in IF signal processing circuit 150 including IF amplifier154, SAW filter 156, and gain-controlled IF amplifier 158. The gain ofgain-controlled IF amplifier 158 is controlled in response to the IF AGCsignal generated by either analog video and sound processing circuit 60(for analog signal reception) or by power detector 179 (for digitalsignal reception). The output signals of gain-controlled amplifier 158apply to the subsequent analog signal processing circuit includinganalog video and sound processing circuit 60 and to subsequent digitalsignal processing circuit 170 including analog-to-digital converter 172,power detector 179, demodulator 174, equalizer 176, and error correctiondecoder 178.

Analog video and sound processing circuit 60 demodulates analogtelevision signals, such as NTSC, PAL and SECAM television signals, andgenerates RF and IF AGC signals which control gain-controlled RFamplifier 124 and gain-controlled IF amplifier 158 respectively inresponse to the quantity (i.e., magnitude) of the RF analog televisionsignals. Analog video and sound processing circuit 60 includes ananalog-to-digital converter and provides microprocessor 50 with theparameter information representing such RF and IF AGC signals as digitaldata. Similarly, analog video and sound processing circuit 60 providesmicroprocessor 50 via the I²C bus with the parameter information indigital form representing automatic chroma control (ACC) signal andpicture-to-sound carrier ratio (P/S), each one of which indicates thedifferent aspects of picture quality of the analog RF televisionsignals.

Digital signal processing circuit 170 processes digital televisionsignals, such as QAM, QPSK, and HD VSB signals. Analog-to-digital (A/D)converter provides digitized IF signals for demodulator 174 and powerdetector 179, both of which are usually located on a digital demodulatorIC. Power detector 172 generates RF and IF AGC signals which controlgain-controlled RF amplifier 124 and gain-controlled IF amplifier 158respectively in response to the quantity (i.e., magnitude) of the RFdigital television signals. Power detector 172 provides microprocessor50 via the I²C bus with the parameter information representing such RFand IF AGC signals. The determination of the AGC level is performedbased upon the digitized IF signals which have not yet been demodulated.

Demodulator 174 demodulates the digitized IF signals from A/D converter172 and provides so-called the “digital base-band signals.” Demodulator174 also generates the parameter information representing thesignal-to-noise ratio (S/N), which indicates one of the aspects ofpicture and sound quality of the RF digital television signals andprovides microprocessor 50 via the I²C bus with such information.

Equalizer 176 receives the digital base-band signals from demodulator174 and attempts to correct their impulse responses. The impulseresponse may be degraded by transmission channel multipath effects asimperfections of the antenna and tuner input circuitry. Equalizer 176also generates the parameter information representing the filter taps,which indicates one of the aspects of the quality of the RF digitaltelevision signals, and provides microprocessor 50 via the I²C bus withsuch information. By monitoring these equalizer taps, the abovecircuitry can be selected to reduce the effects of the antenna and tunerinput imperfections.

The output signals of equalizer 176 apply to error correction decoder178 which performs error correction on the digital base-band signals bythe Reed-Solomon decoding procedure. Error correction decoder 178generates the parameter information representing bit error rate (BER),which indicates one of the aspects of picture and sound quality of theRF digital television signals, and provides microprocessor 50 via theI²C bus with such information.

The output signals of error correction decoder 178 are then processed bythe subsequent signal processing circuit (not shown). Microprocessor 50,via PLL IC 30 and digital-to-analog converter (DAC) IC 40, controls theoperations of boost/attenuator circuit 110 based upon the foregoingvarious parameter information in the manner disclosed in FIG. 3.

FIG. 2 discloses another exemplary implementation of theboost/attenuator circuit 210 in conjunction with an analog/digitaltelevision signal receiver. In this implementation, attenuator 112 withattenuator switch 118 is now placed between RF input 22 and U/V splitter20 so that both the VHF and UHF television signals may be attenuated inresponse to the attenuator control signal generated by PLL IC 30 whichis controlled by microprocessor 50 via the I²C bus. The UHF televisionsignals are filtered by tunable single-tuned (ST) filter 114 and thenamplified by low noise amplifier 116 in response to the boost controlsignal in the same manner as described above in conjunction with FIG. 1.The VHF television signals separated by U/V splitter 20 from the UHFtelevision signals apply to VHF tuner circuit 130 which includes tunablesingle-tuned (ST) filter 132, RF amplifier 134, tunable double-tuned(DT) filter 136, mixer 144, VHF local oscillator 144, and double-tuned(DT) IF filter 152. Double-tuned (DT) IF filter 152 are used for bothVHF and UHF signal processing as a common element. VHF tuner circuit 130converts television VHF signals into television IF signals and isusually located in a tuner module of a television signal receiver. Thefunctions of IF signal processing circuit 150, analog video and soundprocessing circuit 60, and digital signal processing circuit 170 are thesame as those explained above in conjunction with FIG. 1. Microprocessor50, via PLL IC 30 and digital-to-analog converter (DAC) IC 40, controlsthe operation of boost/attenuator circuit 110 based upon the foregoingvarious parameter information in the manner disclosed in FIG. 4.

Referring now to FIG. 3, flow chart 300 discloses an exemplary manner ofoperation of boost/attenuator circuit 110 shown in FIG. 1, which issupplemental or in addition to the various manners of operation of theentire circuit disclosed herein. In step 302, a television tuner istuned to a particular UHF television channel. In step 304,microprocessor 50 retrieves the previously-stored AGC parameter datafrom memory 55. The determination of the AGC level for the individualreceivable channels throughout the entire VHF/UHF television bands isusually performed when a user initially sets up the television signalreceiver, and such individual AGC information can be stored in a memoryto form a so-called “memory scan list.”

In step 306, microprocessor 50 compares the stored AGC level for thetuned channel to a predetermined threshold. If the current AGC level isnot lower than the threshold, then the boost/attenuate circuit 110 willbe bypassed as indicated in step 314. However, if the level is lowerthan the threshold, then in step 308 microprocessor 50 acquires the AGClevels of the adjacent channel signals from memory 55. In step 310, ifone of the adjacent channel AGC levels is stronger than a predeterminedlevel, boost/attenuator circuit 110 is bypassed. If not, in step 312,low-noise amplifier 116 is enabled and applied.

In step 316, the various parameters which indicate the quality of theinformation borne by the tuned UHF television signal, such as EQ taps,BER, SNR, ACC, and P/S, are measured as described above. If suchparameters indicate that signal quality is unacceptable, attenuator 112is enabled and applied as indicated in step 318. If such parametersindicate that signal quality is acceptable, the television signalreceiver continues to receive the tuned signal as indicated in step 326,and the channel data, including the measured parameter data as well asthe present operation mode of boost/attenuator circuit 110 (i.e.,whether or not low-noise amplifier 116 is enabled), for this particularchannel can be stored in memory 55 as indicated in step 328.

In step 320, the foregoing various parameters are again measured todetermine the effect of attenuator 112. If the measured parametersindicate that the picture and/or sound qualities have/has improved,attenuator 112 is continued to be enabled and applied as indicated instep 324. If, however, the parameters indicate that the application ofattenuator 112 does not improve the picture and/or sound qualities, themessage “Channel Not Receivable” is displayed on the screen and suchinformation is stored on memory 50 as indicated in step 322.

Referring now to FIG. 4, flow chart 400 discloses an exemplary manner ofoperation of boost/attenuator circuit 210 shown in FIG. 2, which issupplemental or in addition to the various manners of operation of theentire circuit disclosed herein. In step 402, a television tuner istuned to a particular VHF or UHF television channel. When a VHF channelis tuned, the various parameters which indicate the quality of theinformation borne by the tuned VHF television signal are measured. Morespecifically, these parameters are measured under two different modes ofoperation of boost/attenuator circuit 210. Under the “Normal” mode,attenuator 118 is bypassed so that the VHF television signals directlyapply to tunable single-tuned (ST) filter 132 via U/V splitter 20 asindicated in step 412. Under the “Select Attenuator” mode, attenuator118 is enabled and applied to the VHF television signals as indicated instep 416. The measured parameter data under the respective operationmodes are stored onto memory 55 as indicated in steps 414 and 418.

After measuring the various parameter information, the magnitude of theVHF television signals is determined by evaluating the AGC signals instep 422. If the VHF televisions signals are so weak that they might notbe suitable for proper reception, attenuator 118 is disabled andbypassed as indicated in step 426.

In step 420, the results of the foregoing measurements under thedifferent operation modes are compared, and whichever the mode providesa better picture and/or sound condition is continued to be used. Thatis, if the application of attenuator 118 provides a better pictureand/or sound condition, attenuator 118 is enabled and applied forreception of the tuned channel as indicated in step 424. If not,attenuator 424 is bypassed as indicated in step 426. In step 428, theinformation representing the selected operation mode (i.e., use ornon-use of attenuator 116) for this particular television channel isstored onto memory 55 for the future access to this channel.

When a UHF channel is tuned, the various parameters which indicate thequality of the information borne by the tuned UHF television channel aremeasured under four different operation modes of boost/attenuatorcircuit 210. Under the “Normal” mode, both attenuator 118 and low-noiseamplifier 116 are bypassed so that the UHF television signals directlyapply to tunable single-tuned (ST) filter 122 via U/V splitter 20 asindicated in step 472. Under the “Select Attenuator” mode, attenuator118 is enabled and applied to the UHF television signals but low-noiseamplifier 116 is bypassed as indicated in step 476. Under the “SelectBoost” mode, low-noise amplifier 116 is enabled and applied to the UHFtelevision signals but attenuator 118 is bypassed as indicated in step480. Under the “Select Attenuator+Boost” mode, both attenuator 118 andlow-noise amplifier 116 are enabled and applied to the UHF televisionsignals. The measured parameter data under the respective operationmodes are stored onto memory 55 as indicated in steps 474, 478, 482, and486.

In step 488, all the measurement results under the respective fouroperation modes are compared, and whichever the mode provides the bestpicture and/or sound condition is continued to be used as indicated instep 490. In step 492, the information representing the selected bestoperation of boost/attenuator circuit 210 (i.e., whether or not eitheror both attenuator 118 and low-noise amplifier is or are enabled) forthis particular UHF television channel is stored onto memory 55 for thefuture access to this channel.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

For example, boost/attenuate circuit 110 and its control methods can beused for analog/digital broadcast radio receivers, and boost/attenuatecircuit 110 can be placed anywhere between an antenna and an RF inputpoint of the front-end circuit of a television tuner module. That is,boost/attenuate circuit 110 could be implemented in a television signalreceiver set, could be placed in a separate module external to atelevision signal receiver set, or could be implemented in an antennaassembly.

The term “television signal receiver” used herein includes anytelevision signal receiver with or without display. For example, theterm “television signal receivers” includes but is not limited to videocassette recorders (VCR's), DVD players, and set-top boxes.

1. A signal processing method comprising the steps of: tuning to achannel frequency; measuring the magnitude of a first radio frequency(RF) signal at a first channel frequency; storing said magnitude of saidfirst radio frequency signal in a first memory location; measuring themagnitude of a second radio frequency (RF) signal at a second channelfrequency in the vicinity of said first channel frequency; storing saidmagnitude of said second radio frequency signal in a second memorylocation; and enabling an RF amplifier if the magnitude of said first RFsignal on said first channel frequency is below a first predeterminedthreshold level and the magnitude of a second RF signal at a secondchannel frequency in the vicinity of said first channel frequency isbelow a second predetermined level.
 2. A method of processing a signalcomprising the steps of: tuning to a first channel frequency; measuringthe magnitude of a first radio frequency (RF) signal at said firstchannel frequency; storing said magnitude of said first radio frequencysignal in a first memory location; measuring the magnitude of a secondradio frequency (RF) signal at a second channel frequency in thevicinity of said first channel frequency; storing said magnitude of saidsecond radio frequency signal in a second memory location; and disablingan RF amplifier if either the magnitude of said first RF signal on saidfirst channel frequency is above a first predetermined threshold levelor the magnitude of said second RF signal on said second channelfrequency in the vicinity of said first channel frequency is above asecond predetermined threshold level.